It is well known that many utility installations, for example, sewer pipes, waste water pipes, electric cable conduits, mains water supply control valves, transformers and the like, are positioned below ground level. Access to these utility installations is generally achieved by climbing through an entrance hole at ground level and down a vertically extending access conduit, usually a cylindrical pipe having a diameter large enough to permit at least a person to gain access to the utility installation.
The access conduit entrance is invariably provided with a utility access cover which is usually fabricated from a rigid robust material such as cast iron or reinforced concrete and, as a result, is heavy and difficult to maneuver. Most usually, these utility access covers are fabricated from cast iron and have at least two holes near the outer circumferential edge of the cover for use in removing the cover from the entrance hole. In position, the cover is seated in a cover support ring situated such that the cover and the ring are substantially in the plane of the surrounding surface, such as that of the road or sidewalk surface. The technique usually employed for lifting and maneuvering these covers is to use a crow-bar, trap-hook, or similar metallic rod-like tool by inserting the tool into one of the holes in the cover and pulling the tool outwards and upwards towards the operator, relying on the friction between the cover and the tool to effect lifting of the cover. Alternatively, the cover may be removed by forcing it out of its supporting ring by jamming a tool between the outer peripheral edge of the cover and the support ring. In both instances, very little control over the movement of the cover can be maintained and, furthermore, there is always the chance that the cover may drop off the tool and injure the operator.
U.S. Pat. No. 4,227,731 to Alfred B. Castle, the inventor of the tool of the present application, there is disclosed a lifting tool which can be used to conveniently lift and maneuver utility access covers. The tool is especially suited for lifting and maneuvering heavy cast iron manhole covers since it is possible to maintain complete control over the movement of the cover without risk of the cover being disengaged from the tool and possibly injuring the operator. The tool described in the above-mentioned patent, the disclosure of which is specifically incorporated herein by reference, is particularly suited for lifting and maneuvering utility access covers provided with locking devices such as that described in U.S. Pat. No. 3,751,949 to Alfred B. Castle.
While the lifting tool described in the above-mentioned U.S. Pat. No. 4,227,731 works well for regular-sized circular manhole covers and small gratings, difficulties are still encountered in lifting and maneuvering larger manhole covers and gratings, in particularly those employed, for example, to cover large below-ground-level transformer housings. A major problem with these larger covers and gratings is that, in view of their increased dimensions and weight (typically in the range of 300 to 2,000 pounds, e.g., 450 to 700 pounds), it is generally necessary to employ two or more persons for the cover handling operation, which increases labor cost significantly. In addition, while it may be possible for two or more persons to lift the cover from its retaining frame without the expenditure of too much effort, moving the covers away from the frame requires care and can be dangerous, as it is necessary to walk near the edges of the frame. Loss of control of the cover in the region of the frame could result in severe damage to the utility installation if the cover falls into the installation vault as well as severe physical injury to the persons involved.
In copending application Ser. No. 131,690 (U.S. Pat. No. 4,321,003), the disclosure of which is incorporated by reference in the present application, there is described and claimed a lifting tool which is particularly suited for lifting and maneuvering utility access covers, especially large and heavy utility access covers. The lifting tool of U.S. patent application Ser. No. 131,690 comprises a ring support means for supporting the tool during lifting and maneuvering the object, the ring support means having at least two axially spaced-apart ring assemblies which are spaced-apart by a distance sufficient to permit the object to be lifted and suspended between the ring assemblies. Each ring assembly includes an inner and outer concentric ring member, each being independently rotatable with respect to the other, with the inner ring member being at least partially axially within the outer ring member. A connecting means is mounted on the inner ring members for axially connecting together the spaced-apart ring assemblies, and hooks or other object engaging means are mounted on the connecting means for liftingly engaging the tool with the object to be lifted. Lifting is effected by engaging a lever to the connecting means so that when a force is applied to the lever to move the connecting means in a generally upward direction, the inner ring members are rotated simultaneously with respect to the outer ring members which remain substantially stationary. Upon simultaneous rotation of the inner ring members, the object is vertically lifted into a raised position between the ring assemblies as the connecting means and the hooks move upwardly. With the object suspended in the raised position, the object is transportable by pulling or pushing the lever means to effect rotation of the outer ring members relative to the inner ring members. The object is lowered by moving the lever in the opposite direction to that just described, whereby the inner ring members rotate in the opposite direction and permit lowering of the suspended object back to ground level or into a receiving frame.
While the above-describing lifting tool operates very well in practice, it has been found that when the tool is used for lifting very heavy objects such as wide utility access grating covers, the connecting means extending between the two ring assemblies occasionally undergoes bending or flexing which can interfere with the vertical movement of the object, and thereby impede the lifting operation.